Insulated filament supports

ABSTRACT

A new type of support for filaments in incandescent lamps and vacuum tubes is disclosed. The support is nonconductive, able to resist high temperatures, rigid, malleable, and it eliminates variation in rating and stability of rating in lamps and tubes caused by filament contact with the support.

United States Patent Nickolas P. Dumas (Zranlord. NJ.

Dec. 21 1 97 l Wagner Electric Corporation Inventor Appl. No. FiledPatented Assignee INSULATED FILAMENT SUPPORTS 5 Claims, 3 Drawing Figs.

US. Cl 313/277,

313/257, 313/289, 313/352 Int. Cl H0lj 1/90 Field of Search 313/276,

[56] References Cited UNITED STATES PATENTS 1,047,541 12/1912 Ledever313/277 X 1,203,635 11/1916 Ledever 313/277 2,191,331 2/1940 Van Liempt.313/277 2,945,978 7/1960 Hodge 313/276 X Primary Examiner-DavidSchonberg Assistant Examiner-Toby H. Kusmer Attorney-Eyre, Mann & LucasABSTRACT: A new type of support for filaments in incandescent lamps andvacuum tubes is disclosed. The support is nonconductive, able to resisthigh temperatures, rigid, malleable, and it eliminates variation inrating and stability of rating in lamps and tubes caused by filamentcontact with the sup port.

PATENIEB m2! an INVENTOR N/CKOLAS I? DEMAS IY a n... ('M

A TTOR/VEYS INSULATED FILAMENT SUPPORTS The present invention relates toa new type of support for incandescent lamps and vacuum tubes which isrigid, malleable, nonconductive and capable of withstanding hightemperatures.

Incandescent lamps and vacuum tubes which contain a filament usuallyhave some type of support at one or more places on the filament to avoidthe phenomenon known as microphonism. Microphonism is an undesirablephenomenon which results from a vibration of the filament. When themicrophonism is in an audio circuit, such as a radio, the vibratingfilament causes an audible sound which is annoying. To counteract this,a support is used to divide the filament into sections, each of which isrelatively short. This reduces the length of the filament which is freeto vibrate and thereby eliminates the microphonism.

The most desirable type of support is one which is rigid, yet malleableand capable of withstanding high temperatures. As a result, metallicsupports are usually employed. The disadvantage of standard metallicsupports is that they conduct electricity and thus can cause a shortcircuiting of the filament which results in variations in rating and inthe stability of rating of the lamp, especially when the lamp issubjected to vibration such as in automobile radios. A plurality ofturns of the filament can come into contact with the support and, if thefilament is thus touching the support at more than one point, thefilament may be shorted out at two or more points of contact. Thiseffectively changes the length of the filament by shortening it whichchanges the rating of the lamp or tube in which the filament isemployed. The lamp or tube will thus exhibit noise," which is avariation in rating or in stability of rating.

Numerous methods of insulating the supports have been tried in order toeliminate this short circuiting, but none of these are satisfactoryeither because of high cost or difficulty of application. The majorproblem is the high temperature in an inert atmosphere which the supportmust withstand. The temperature is frequently in the neighborhood of1,800" C. and the atmosphere is usually argon or a vacuum. Standardinsulating materials either will not withstand this high temperature inan inert atmosphere, or, if they will, they do not have the desiredproperties of being strong, rigid and malleable. Aluminum oxide, forexample, while it will withstand the high temperatures in air, will notwithstand them in an inert atmosphere. Ceramics, n the other hand, willwithstand the high temperatures in an inert atmosphere, but they are notmalleable and are therefore difficult to work with. Additionally,ceramics and other similar insulating materials applied to a metalliccore will usually prove unsatisfactory because of their tendency toflake off when the core is formed into its desired shape.

We have now discovered an insulated support which eliminates all of theabove-mentioned disadvantages but yet retains the properties of beingstrong, rigid, malleable and capable of withstanding high temperatures.The support comprises a tantalum oxide coating on a core such as ametal. For best results a metallic support is employed made with atantalum metal or tantalum alloy for high strength and durability. Thetantalum oxide coating is nonconductive even at high temperatures ininert atmospheres, and it eliminates the possibility of short circuitingthe filament and causing noise.

The tantalum oxide coating is preferably formed by oxidizing a tantalumor tantalum alloy strip of wire, thereby forming the tantalum oxidecoating as an integral part of the support. The preferred method offorming the tantalum oxide coating is to anodize the selected tantalumwire in conventional manner as for example at about 600 volts in acitric acid bath. The anodization is continued until the flow of currentapproaches 0 amperes due to the formation of the tantalum oxide coating,which is nonconductive. A spool of tantalum wire may be continuouslycoated by anodization by passing it through a citric acid bath at a ratewhich will forma substantially nonconductive tantalum oxide coatingthereon.

The tantalum oxide coating may completely surround the support, or itmay be only at the point where the support and the filament come intocontact. Additionally, it may cover the entire support or only a sectionor sections of it, as desired.

We have found that the tantalum oxide coated support is especiallyuseful in anchor type supports. Anchor supports are used to break thefilament up into segments. Each anchor is usually held firmly in place,as by means of a glass bead. This type of support is most frequentlyused in incandescent lamps and vacuum tubes.

The tantalum oxide coated support has many useful applications, and isnot limited to use in incandescent bulbs or vacuum tubes. It may be usedin any application where it is desired to have a nonconductive supportfor a relatively long filament or other current carrying member. It mayalso be used either as a rigid support, as in an anchor, or as a freefloating support, for example, as a separator between two filaments. Inthis application it could be held in place only by contact with thefilaments.

These and other features of the present invention may be more fullyunderstood by reference to the drawings, in which the same number isused to identify identical parts of the structure, and in which:

FIG. 1 shows an incandescent lamp with anchor wires;

FIG. 2 shows a filament in contact with the anchor wire where theyinterconnect; and

FIG. 3 shows a filament in contact with the point of interconnection andanother point on the anchor.

FIG. 1 is an example of a standard incandescent lamp [0 in which anchors12 are employed. Anchors are desireable in this bulb because of thelength of the filament 14. If the clamps 16 which hold the filament 14were separated so that the filament 14 was taut, the filament wouldextend over quite a length. Any vibration of a filament this long wouldcontinue for quite a while due to the length of the filament and wouldresult in the phenomenon known as microphonism. The anchors which areinserted along the length of the filament 14 divide the filament intosections, each of which is relatively short thereby eliminating a longfree-standing length of filament which would tend to vibrate. Both theclamps l6 and the anchors 12 are maintained in position by a glass head18.

FIG. 2 is an enlarged view of the interconnection of the filament 14with the anchor 12. The anchor 12 has been cut away so that the filament14 may be more clearly seen. Points 22, 24, 26, 28 and 30 on filament 14are representative of the turns of the filament. As shown, points 24, 26and 28 are in contact with the anchor 12 and, if the anchor isconductive, there will be a short circuit between points 24 and 28 whichwill result in a shortening of the effective length of the filament,thereby creating the phenomenon known as noise. If there is vibration ofthe lamp, as by road vibration in an automobile, the filament will tendto vibrate and as it vibrates it is possible for points 22 and 30 toalso come in contact with the anchor 12, thereby causing an even shorterefiective length and therefore even greater noise. In accordance withthe present invention, the anchor is made nonconductive by the formingof a tantalum oxide coating 32 on the tantalum core 34 of the anchor 12.When the turns 22, 24, 26, 28 and 30 of the filament 14 come in contactwith the tantalum oxide coating 32 there is no short circuiting sincethe tantalum oxide coating is nonconductive. Since there is no shortcircuiting, there is no noise, and, hence, there is no variation inrating or in stability of rating.

FIG. 3 illustrates another type of short circuiting which can occurbetween the filament 14 and the anchor 12. Here, the filament 14 is incontact with the anchor 12 at point 26 and also farther down the anchorat point 36. This causes short circuiting between points 26 and 36 andresults in the creation of noise. This short circuiting can be avoidedby using the anchor of the present invention, which can be insulatedthroughout its length if desired. The insulated anchor is not conductiveand therefore there will be no short circuiting between points 26 and 36of the filament'l4 even'when these points 26 and 36 are in contact withthe anchor 12. Note that if there is no nonconductive coating it is alsopossible for the filament to be short circuited from point 36 on oneanchor to point 36 on the other anchor, thereby effectively eliminatingmost of the useful length of the filament, and creating a substantialvariation in rating of the lamp.

It will be understood that it is intended to cover all changes andmodifications of the preferred embodiment of invention herein chosen forthe purpose of illustration which do not constitute departure from thespirit and scope of the invention.

What is claimed is:

l. A malleable support for current-carrying members having a tantalumoxide coating on at least a portion thereof said coating beingsubstantially nonconductive and stable at temperatures of l,800 C. in aninert atmosphere.

2. The support of claim 1 wherein the current-carrying member is afilament.

3. The structure of claim 1 in which the support is a metallic tantalum.

4. A method of producing malleable nonconductive supports forcurrent-carrying members which comprises oxidizing at least a portion ofa tantalum support thereby forming a tantalum oxide coating on at leasta portion of said support, said coating being substantiallynonconductive to electricity and stable at temperatures of l ,800" C. inan inert atmosphere.

5. A substantially nonconductive malleable anchor support for filamentsin incandescent lamps which comprises a tantalum support at least aportion of which has a tantalum oxide coating thereon, said coatingbeing substantially nonconduc tive to electricity and stable attemperatures of 1,800" C. in an inert atmosphere.

1. A malleable support for current-carrying members having a tantalumoxide coating on at least a portion thereof said coating beingsubstantially nonconductive and stable at temperatures of 1,800* C. inan inert atmosphere.
 2. The support of claim 1 wherein thecurrent-carrying member is a filament.
 3. The structure of claim 1 inwhich the support is a metallic tantalum.
 4. A method of producingmalleable nonconductive supports for current-carrying members whichcomprises oxidizing at least a portion of a tantalum support therebyforming a tantalum oxide coating on at least a portion of said support,said coating being substantially nonconductive to electricity and stableat temperatures of 1,800* C. in an inert atmosphere.
 5. A substantiallynonconductive malleable anchor support for filaments in incandescentlamps which comprises a tantalum support at least a portion of which hasa tantalum oxide coating thereon, said coating being substantiallynonconductive to electricity and stable at temperatures of 1,800* C. inan inert atmosphere.